Hybrid cords are threadlike reinforcement elements that are used for example in industrial rubber products and (pneumatic) vehicle tires.
Hybrid cords are sufficiently known to persons skilled in the art and are characterized in that the at least two yarns of this hybrid cord consist of different materials. As a result, the physical properties of the hybrid cord can be set on the one hand via the targeted selection of material of the individual yarns and on the other hand via their construction.
DE 10 2009 003 359 AI, for example, has disclosed a hybrid cord for use in a pneumatic vehicle tire that consists of a rayon multifilament yarn and a PET multifilament yarn. The yarn linear density of the rayon multifilament yarn is 1840 dtex, and the yarn linear density of the PET multifilament yarn is 1440 dtex. The hybrid cord has a diameter commonly used to date. The rayon multifilament yarn is classed with viscose multifilament yarns.
However, due to reasons of cost savings, an effort is made to use reinforcement elements with smaller diameters, although these reinforcement elements should have approximately the same physical properties as reinforcement elements with a conventional diameter.
An effort is also made to use renewable raw materials whenever possible.
Cellulose is the most frequently encountered and most important naturally occurring polymer. In addition to cellulosic shaped bodies, like paper, blown films, cellophane, and sponge cloths, cellulosic fibers are considered among the most important industrial products and are used primarily for clothing purposes, as insulating materials and as industrial reinforcement elements.
Cellulosic fibers, filaments and multifilaments can be obtained in a wide variety of ways and in different forms which are also known to persons skilled in the art. The most common processes are the so-called regeneration processes in which cellulose is first converted chemically into soluble unstable or easily saponifiable derivatives and dissolved. For example, cellulose acetate, cellulose formate, or cellulose carbamate are known as soluble derivatives from which cellulose can be regenerated. In the most important method, the viscose method, the unstable derivative is a cellulose xanthogenate, and the yarns produced using the viscose method are known as viscose or rayon yarns. In the viscose method, the solution is pumped through spinnerets and regenerated to form viscose filaments in a coagulation bath, washed and sized (and functionally coated if necessary) in one or more post-treatment steps, and subsequently wound up on endless bobbins or processed into cut fibers. More recently, however, cellulosic fibers in the form of chopped fibers are also being used increasingly in thermoplastic reinforcement, e.g. in PP/rayon composite materials, in the form of uni- and bidirectional woven fabrics, and also for reinforcing duromers such as epoxy resins.
High-tenacity cellulosic multifilament yarns with low yarn linear density, i.e. a smaller yarn diameter, are known as such.
For example, ultra-high-tenacity yarns made of cellulose formate and cellulose modified by formaldehyde with a low overall linear density are known. For example, cellulose formate fibers are described in patent publication U.S. Pat. No. 6,261,689 which were conditioned at a temperature of (20±2)° C. and a relative humidity of (65±2)%, defined as a standard climate according to EN ISO 20139 (currently: DIN EN ISO 139), and have an overall linear density of 460 dtex and a tenacity of 76 cN/tex.
Patent publication U.S. Pat. No. 3,388,117 describes cellulosic fibers modified by formaldehyde with an overall linear density of 485 dtex and a conditioned tenacity of 78 cN/tex.
Not described in the prior art, however, are high-tenacity viscose multifilament yarns with an overall linear density <1100 dtex.
While GB 685,631 B describes rayon yarns, i.e. viscose multifilament yarns made of 100 individual filaments with a low overall linear density of 100 den (110 dtex), they have a conditioned tenacity of only 2.3 g/den (20.4 cN/tex) and a tenacity in the oven-dried state of 2.9 g/den (25.6 cN/tex). In a further example, GB 685,631 B discloses yarns with a yarn linear density of 400 den (440 dtex) having 260 filaments and moderate tenacities of 4.1 g/den (36.2 cN/tex) in the conditioned viscose multifilament yarn and 5.3 g/den (46.8 cN/tex) in the oven-dried viscose multifilament yarn.